1. Field of the Invention
The invention relates in general to a backlight module and more particularly to a backlight module with heat-radiating design.
2. Description of the Related Art
Along with the rapid advance in the manufacturing technology of liquid crystal display (LCD) and its advantageous features of compactness, energy saving and low radiation, LCD has now been widely applied in various electronic products such as personal digital assistant (PDA), notebook computer, digital still camera, mobile phone, computer monitor screen and liquid crystal TV. Further due to the gorgeous input in R&D and the adoption of large scale production facilities, LCD is experiencing a continual quality improvement and price reduction. Consequently, the application of LCD is getting more and more popular. Since LCD panel is not self-luminous, the LCD still needs to have a backlight module to provide necessary light for display purpose.
Referring to FIG. 1A, a partial top view of a conventional backlight module, and FIG. 1B, a front view of the backlight module illustrated in FIG. 1A, at the same time. In FIG. 1A and FIG. 1B, backlight module 10 at least includes a bezel 12, a reflector sheet 14 and plural straight type cold cathode fluorescent lamps (CCFLs) 16. Bezel 12 includes a body portion 12a, a first supporting portion 12b, and a second supporting portion 12c. Of which, body portion 12a has a body portion's top face 12d. First supporting portion 12b and second supporting portions 12c are disposed at the two ends of body portion's top face 12d. The top end of first supporting portion 12b has plural slots 17b while the top end of second supporting portion 12c has plural slots 17c. Reflector sheet 14 is disposed on body portion's top face 12d but is located between first supporting portion 12b and second supporting portion 12c. It is noteworthy that other reflecting materials can also be disposed on the inner surface of the first and the second supporting portions 12b and 12c which are connected with body portion's top face 12d. Each of CCFLs 16 includes a luminous section 16a and two electrode portions 16b and 16c, wherein luminous section 16a connects electrode portions 16b and 16c. Each electrode portion 16b at each of CCFLs 16 is disposed at slot 17b of first supporting portion 12b, while each electrode portion 16c at each of CCFLs 16 is disposed at slot 17c of second supporting portion 12c. CCFLs 16 are disposed on bezel 12 with reflector sheet 14 disposed underneath.
When a high voltage is applied onto electrode portions 16b and 16c, electrons are ejected toward luminous section 16a from electrode portions 16b and 16c to collide with the mercury inside luminous section 16a. Following the collision triggered by high-voltage accelerated electrons, mercury will return to a stable status from an unstable status in an instant and will release extra energy in the form of 253.7 nm ultraviolet light. When absorbed by the fluorescent powder on the inner wall of luminous section 16a, the ultraviolet light will be transformed into visible light and emitted outside CCFLs 16.
It is noteworthy that when CCFLs 16 are emitting the light, heat will be generated inside the tubes which will boost the temperatures at the tube wall up. Since mercury concentrates better at low temperatures, it becomes more and more difficult for mercury to concentrate at luminous section 16a as the temperatures at the tube wall are getting higher and higher. Consequently, the mercury at CCFLs 16 will diffuse towards electrodes 16b and 16c and will be deposited there due to sputter effect. This severely affects the electricity quality of electrode portions 16b and 16c, resulting in a shorter lifetime of CCFL 16 and a poorer luminance quality of backlight module 10.